Historically Based Perspective on the Immunotherapy of Type 1 Diabetes: Where We Have Been, Where We Are, and Where We May Go

<b>Systematic Background/Objectives:</b> Type 1 diabetes mellitus (T1DM) is an autoimmune condition in which pancreatic β-cells are selectively destroyed, predominantly by autoreactive T lymphocytes. Despite decades of research, the achievement of durable immune tolerance remains elusive. This review presents a historically grounded and forward-looking perspective on the evolution of immunotherapy in T1DM, from early immunosuppressive interventions to advanced precision-based cellular approaches. Specifically, we focus on systemic immunosuppressants (e.g., corticosteroids, cyclosporine), monoclonal antibodies (e.g., anti-CD3, anti-IL-1, anti-TNF), regulatory cell-based approaches (e.g., Tregs, CAR-Tregs, MDSCs), and β-cell replacement strategies using stem cell-derived islets. <b>Methods:</b> We analyzed major clinical and translational milestones in immunotherapy for T1DM, with particular attention to the transition from broad immunosuppression to targeted modulation of immune pathways. Emerging data on cell-based therapies, artificial intelligence (AI)-driven stratification, and personalized intervention timing have been incorporated to provide a comprehensive overview of current and future directions. <b>Results:</b> Initial therapies such as corticosteroids and cyclosporine offered proof-of-concept for immune modulation, yet suffered from relapse and toxicity. The introduction of monoclonal antibodies (e.g., teplizumab) marked a shift toward immune-specific intervention, particularly in stage 2 preclinical T1DM. More recent approaches include low-dose IL-2, checkpoint modulation, and antigen-specific tolerance strategies. Cellular therapies such as Treg adoptive transfer, chimeric antigen receptor Tregs (CAR-Tregs), and stem cell-derived islet replacements (e.g., VX-880) have shown promise in preserving β-cell function and modulating autoimmunity. Myeloid-derived suppressor cells (MDSCs), although still preclinical, represent a complementary avenue for immune tolerance induction. Concurrently, AI-based models are emerging as tools to stratify risk and personalize immunotherapeutic timing, enhancing trial design and outcome prediction. <b>Conclusions</b>: In conclusion, the historical progression from broad immunosuppression to precision-driven strategies underscores the importance of stage-specific, mechanism-based interventions in T1DM. The convergence of targeted biologics, regenerative cell therapies, and β-cell replacement approaches, supported by AI-enabled patient stratification, offers a realistic path toward durable immune tolerance and functional β-cell preservation. Continued integration of these modalities, coupled with rigorous long-term evaluation, will be essential to transform these scientific advances into sustained clinical benefit.